Research On Karst Collapse Mechanism And Prevention Countermeasures In Kunming New Airport

Kunming new international airport is located in Guandu area,24km northeast to Kunming.The exploration area is about 18507237.3m².Planning and construction east-west two parallel runways to the current period.The construction scale conforms to B-747 and A-340,airport grade is 4F.Kunming new airport is a large-scale hub-airport,Which is an important project of China that oriented to international large channel in Southeast Asia.This will play an important role in promoting building of China-ASEAN Free Trade Area and regional economic cooperation in Great Mekong River Basin.Meanwhile the construction of new airport will provide more convenient air transportation for better development of Yunnan economy.The landform in Kunming new airport,as a whole,mainly is karst,secondly the tectonic denudation hills and alluvial depositional.For the outcrop in field region which mainly is Palaeozoic formation includes Cambrian,Devonian,Permian and Carboniferous.In this area about 80%are carbonate rocks,the lithology mainly are dolomite and limestone.Study area is located in compound position of multi-group Structures.The fold structure mainly are Zhuanshan anticline,Shiquansi and Hunshuitang syncline.And faults structure mainly are Yangtaoqing～Sujiafen fault (F₁₀),Baihanchang～Xichong fault(F₁₂),Hebaodi～Wusazhuangnan fault(F₁₈¹) and Huaqing～Libaichong fault(F₁₈³).Fault structure in field region has not been activity since the Late Pleistocene,so the field region is stable.Joint fissure in Rock Mass is development,Karst middle to strongly developed,Karst development on the surface are mostly karst depression and funnel,underground mainly are stone forests, Karst cave,soil cave and so on.Karst collapses are comparatively developed,on the surface which is divided into bedrock and soil layer collapse,mainly with soil layer collapse. Information obtain by data collecting and study on spot indicate that the complicated karst and collapse development in study area will control the stability of the rock mass of runway,airport building and apron which are the key area in planning airport,also them will influence on other construction area.Because of those, By many investigation and data collection,the paper systematically analyzes engineering geology environmental condition of regional and field region in Kunming new airport,especially,the paper deeply studied the development law of karst and collapse,induction and summarization on the geological generalization mode of soil layer about karst subsidence,deeply studied the karst collapse mechanism and summarized the macro-characteristics of collapse stability in study area,analysis of stability of potential karst cave collaps.Comprehensive various of influencing factors to risk zoning of collapse.Karst collapse countermeasures were studied in order to provide science datum for control engineering,and elicited several achievements:(1)Karst and collapses in study area mainly are development in karst and alluvial depositional landforms,tectonic denudation hills don't develop.(2)The development of surface and underground karst have stages of development in time and spatial difference.Development of funnel and depression on the surface mainly show irregular ellipse,sub-circular,narrow and long shape.The size and depth of funnel and depression are different,which are moniliform development features.Karst caves that are exposed by drilling and geophysical prospecting interpret in study area mainly with monolayer,minority is double and multilayer.The height of karst caves is most 1～3m,and more packed fully or partly. Analysis and research of karst cave have shown that there is no significantly control elevation,but there is a regular pattern in each engineering geological zones:â… zone which the development elevation of karst cave roof is 2070～2080m,â…¡zone which the development elevation of karst cave roof is 2050～2070m and 2090～2199.4m,â…¢zone which the development elevation of karst cave roof is 2070～2090m,â…£zone which the development elevation of karst cave roof is 2050～2080m,â…¤zone which the development elevation of karst cave roof is 2070～2080m and 2090～2137m,â…¥zone which the development elevation of karst cave roof is 2050～2070m,â…¦zone which the development elevation of karst cave roof is 2050～2074m.Different elevations corrosion platform formed in the early stage of karst development.Drilling has revealed that networks of karst conduit and filling of sandy gravel connected funnel of corrosion platform and discharge area.Through analyzing the structure and composition of sandy gravel,we can get conclusion that the early stage of karst is quite developed.(3)Karst collapse in study area which can be divided into nature and man-made collapse according to inducing factors.The planar features of collapse have circular, ellipse,long strip,irregular shape and composite shape.The profile features of collapse have jar shape,well shape,funnel and dish shape.(4)Karst development laws in study area are mainly controlled by the induced fracture network,which mainly are along nearly EW,running N55°W and running N15°W;through tectonic line which are mainly along Hunshuitang and Shiquansi syncline,F₁₀,F₁₀²,F₁₈¹fault.AlsO front of Zhang jia po piedmont proluvial fan(as this) investigation)is concentrated area of karst development(5)The great randomness of collapse development at study area is related to overburden thickness,the surface water and groundwater activity.Meanwhile,the development of fault,fold,fracture at project area control and influence karst collapse development.The Occurrence of collapse development is frequent in June,July with rainwater and January,February with snow and rain.(6)There are six geologic generalization modes of research zone about karst subsidence,Mainly is the mode of "red clay or residual red clay+carbonate rock+ Karst cave".(7)The mechanism of bedrock collapse at study area mainly is earthquake and gravitational.The mechanism of soil layer collapse is mainly caused by seepage pressure,by infiltration of surface water,by lowering of groundwater that has the negative pressure absorption and increase of load,by the dynamic loading and so on.(8)After disasters dangers study by zones,basically stable areas of research zones are about 90%,extremely unstable area to local unstable area contain less,the general stability of the field is better.(9)The thinking of karst collapse in study area mainly are "early prediction, prevention first,key harnessing second,prevention and treatment integrated".The treatment measures for karst collapse of unstable region are closed and anti-seepage of surface,ground strengthening and leap of structure.